The present invention relates to copolymers based on unsaturated monocarboxylic or dicarboxylic acid derivatives and oxyalkylene glycol alkenyl ethers, a process for preparing them and the use of these copolymers as additives for aqueous suspensions of inorganic or organic solids.
It is known that additives in the form of dispersants are often added to aqueous slurries of pulverulent inorganic or organic substances such as clays, porcelain slips, silicate flour, chalk, carbon black, ground rock, pigments, talc, polymer powders and hydraulic binders for improving their processability, i.e. kneadability, spreadability, sprayability, pumpability or flow. These additives, which generally contain ionic groups, are able to break up agglomerates of solids, disperse the particles formed and in this way improve the processability of, in particular, highly concentrated suspensions. This effect is also exploited in a targeted manner in the production of building material mixtures based on cement, lime and hydraulic binders based on calcium sulfate, optionally in a mixture with organic (e.g. bituminous) components and also for ceramic compositions, refractory compositions and oilfield chemicals.
To convert these building material mixtures based on the abovementioned binders into a ready-to-use, processable form, it is generally necessary to use significantly more make-up water than would be necessary for the subsequent hydration or curing process. The voids formed in the component as a result of later evaporation of the excess water leads to significantly impaired mechanical strengths and stabilities.
To reduce this excess water content at a given processing consistency and/or to improve the processability at a given water/binder ratio, use is made of additives which are generally referred to as water reduction agents or fluidizers. Known agents of this type are, in particular, polycondensation products based on naphthalenesulfonic or alkylnaphthalene-sulfonic acids (cf. EP-A-0 214 412) or melamine-formaldehyde resins containing sulfonic acid groups (cf. DE-C 16 71 017).
A disadvantage of these additives is the fact that their excellent fluidizing action, especially in concrete construction, is maintained over only a short period of time. The deterioration in the processability of concrete mixtures (xe2x80x9cslump lossxe2x80x9d) in a short time can lead to problems especially where there is a long period of time between make-up and installation of the fresh concrete, for example as a result of long conveyance and transport paths.
An additional problem arises when such fluidizers are employed in mining and in interior applications (drying of cardboard-faced plasterboard, anhydrite screed applications, manufacture of finished concrete components), since release of the toxic formaldehyde present in the products as a result of the manufacturing method can occur and thus lead to considerable occupational hygiene problems. For this reason, attempts have already been made to develop formaldehyde-free concrete fluidizers based on maleic monoesters and styrene, for example as described in EP-A-0 306 449. The flow of concrete mixtures can be maintained over a sufficiently long period of time by means of these additives, but the original, very high dispersant action is lost very quickly after storage of the aqueous fluidizer formulation as a result of hydrolysis of the polymeric ester.
This problem does not occur in the case of fluidizers based on alkylpolyethylene glycol allyl ethers and maleic anhydride as described in EP-A-0 373 621. However, these products are, like those described above, surface-active compounds which introduce undesirably high proportions of air pores into the concrete mixture, resulting in deterioration in the finished state [sic] and stability of the cured building material.
For this reason it is necessary to add antifoams such as tributyl phosphate, silicone derivatives and various water-insoluble alcohols in concentrations of from 0.1 to 2% by weight, based, on the solids content, to the aqueous solutions of these polymeric compounds. Mixing-in these antifoam components and maintaining a storage-stable homogeneous form of the corresponding formulations is very difficult even when these antifoams are added in the form of emulsions.
The problem of demixing can be solved by complete or at least partial incorporation of a foam-inhibiting or air-repellant structural unit into the copolymer, as described in DE 195 13 126 A1.
However, it has been found that the high effectiveness and the low xe2x80x9cslump lossxe2x80x9d of the copolymers described here often leads to unsatisfactory 24-hour strengths of the concrete. Furthermore, such copolymers do not have optimum properties, especially where a particularly dense and therefore high-strength and high-stability concrete is to be produced using the lowest possible proportion of water and steam curing (finished parts industry) for accelerating the curing process is to be dispensed with.
It is therefore an object of the invention to provide new copolymers which do not have the abovementioned disadvantages of the known agents, i.e. which maintain the processability of highly concentrated building material mixtures for an appropriate length of time even in small amounts and at the same time give an increased strength in the cured state of the building material due to a drastic decrease in the water/binder ratio.
This object is achieved according to the invention by copolymers based on radicals of unsaturated mono-carboxylic or dicarboxylic acid derivatives and oxyalkylene glycol alkenyl ethers, which are characterized in that they comprise
a) from 51 to 95 mol % of structural units of the formula Ia and/or Ib and/or Ic 
xe2x80x83where R1=hydrogen or an aliphatic hydrocarbon radical having from 1 to 20 carbon atoms,
X=OaM, xe2x80x94Oxe2x80x94(CmH2mO)nxe2x80x94R2, xe2x80x94NHxe2x80x94(CmH2mO)nxe2x80x94R2,
M=hydrogen, a monovalent or divalent metal cation, an ammonium ion or an organic amine radical,
a=xc2xd or 1,
R2=hydrogen, an aliphatic hydrocarbon radical having from 1 to 20 carbon atoms, a cycloaliphatic hydrocarbon radical having from 5 to 8 carbon atoms, a substituted or unsubstituted aryl radical having from 6 to 14 carbon atoms,
Y=O, NR2,
m=2 to 4 and
n=0 to 200,
b) from 1 to 48.9 mol % of structural units of the general formula II 
xe2x80x83where
R3 is hydrogen or an aliphatic hydrocarbon radical having from 1 to 5 carbon atoms,
p is from 0 to 3
xe2x80x83and R2, m and n are as defined above,
c) from 0.1 to 5 mol % of structural units of the formula IIIa or IIIb 
xe2x80x83where
S=H, xe2x80x94COOaM, xe2x80x94COOR5, 
xe2x80x94Wxe2x80x94R7 
xe2x80x94COxe2x80x94[NHxe2x80x94(CH2)3]sxe2x80x94Wxe2x80x94R7 
xe2x80x94COxe2x80x94Oxe2x80x94(CH2)zxe2x80x94Wxe2x80x94R7 
xe2x80x94(CH2)zxe2x80x94Vxe2x80x94(CH2)zxe2x80x94CH=CHxe2x80x94R2 
xe2x80x94COOR5 in the case of S=xe2x80x94COOR5 or COOaM
U1=xe2x80x94COxe2x80x94NHxe2x80x94, xe2x80x94Oxe2x80x94, xe2x80x94CH2Oxe2x80x94
U2=xe2x80x94NHxe2x80x94COxe2x80x94, xe2x80x94Oxe2x80x94, xe2x80x94OCH2xe2x80x94
V=xe2x80x94Oxe2x80x94COxe2x80x94C6H4xe2x80x94COxe2x80x94Oxe2x80x94 or xe2x80x94Wxe2x80x94
R4=H, CH3,
R5=an aliphatic hydrocarbon radical having from 3 to 20 carbon atoms, a cycloaliphatic hydrocarbon radical having from 5 to 8 carbon atoms, an aryl radical having from 6 to 14 carbon atoms, 
r=2 to 100
s=1, 2
z=0 to 4
x=1 to 150
y=0 to 15 and
d) from 0 to 47.9 mol [lacuna] of structural units of the general formula IVa and/or IVb 
xe2x80x83where a, M, X and Y are as defined above.
It has surprisingly been found that very small amounts of the copolymers of the invention based on unsaturated monocarboxylic or dicarboxylic acid derivatives and oxyalkylene glycol alkenyl ethers added to aqueous building material suspensions give the suspensions excellent processing properties without delaying strength development. It was particularly surprising that a drastic decrease in the water/binder ratio still leads to highly fluid building materials when the copolymers of the invention are added and no segregation of individual constituents of the building material mixture occurs.
The copolymers of the invention comprise at least three, but preferably four, structural units a), b), c) and d). The first structural unit a) is a monocarboxylic or dicarboxylic acid derivative having the general formula Ia, Ib or Ic. 
In the case of the monocarboxylic acid derivative Ia, R1 is hydrogen or an aliphatic hydrocarbon radical having from 1 to 20 carbon atoms, preferably a methyl group. X in the structures Ia and Ib is xe2x80x94OaM and/or xe2x80x94Oxe2x80x94(CmH2mO)nxe2x80x94R2 or xe2x80x94NHxe2x80x94(CmH2mO)nxe2x80x94R2, where M, a, m, n and R2 are defined as follows:
M is hydrogen, a monovalent or divalent metal cation, ammonium, an organic amine radical, and a=xc2xd or 1 depending on whether M is a monovalent or divalent cation. Organic amine radicals are preferably substituted ammonium groups derived from primary, secondary or tertiary C1-20-alkylamines, C1-20-alkanolamines, C5-8-cycloalkylamines and C8-14-arylamines. Examples of suitable amines from which these radicals are derived are methylamine, dimethylamine, trimethylamine, ethanolamine, diethanolamine, triethanolamine, methyldiethanolamine, cyclohexylamine, dicyclohexylamine, phenylamine, diphenylamine in the protonated (ammonium) form.
R2 can be hydrogen, an aliphatic hydrocarbon radical having from 1 to 20 carbon atoms, a cycloaliphatic hydrocarbon radical having from 5 to 8 carbon atoms, an aryl radical having from 6 to 14 carbon atoms which may also be substituted, m=2 to 4 and n=0 to 200. The aliphatic hydrocarbon radicals can be linear or branched and saturated or unsaturated. Preferred cycloalkyl radicals are cyclopentyl or cyclohexyl radicals, preferred aryl radicals are phenyl or naphthyl radicals which may also be substituted by groups such as xe2x80x94CN, xe2x80x94COOR1, xe2x80x94R1, xe2x80x94OR1 and preferably by hydroxyl, carboxyl or sulfonic acid groups.
In place of or in addition to the dicarboxylic acid derivative of the formula Ib, the structural unit a) (monocarboxylic or dicarboxylic acid derivative) can also be present in cyclic form corresponding to formula Ic, where Y=O (acid anhydride) or NR2 (acid imide) with the above-described meanings for R2.
The second structural unit b) corresponds to formula II 
and is derived from oxyalkylene glycol alkenyl ethers. m, n and R2 are as defined above. R3 is hydrogen or an aliphatic hydrocarbon radical having from 1 to 5 carbon atoms which may be linear or branched or saturated or unsaturated. p can be from 0 to 3.
In the formulae Ia, Ib and II, m is preferably 2 and/or 3 so that the structural units are polyalkylene oxide groups derived from polyethylene oxide and/or polypropylene oxide. In a further preferred embodiment, p in formula II is 0 or 1, i.e. the structural units are vinyl and/or alkyl polyalkoxylates.
The third structural unit c) corresponds to the formula IIIa or IIIb 
In the formula IIIa, R4 can be H or CH3 depending on whether the structural units are acrylic or methacrylic acid derivatives. S can be xe2x80x94H, xe2x80x94COOaM or xe2x80x94COOR5, where a and M are as defined above and R5 is an aliphatic hydrocarbon radical having from 3 to 20 carbon atoms, a cycloaliphatic hydrocarbon radical having from 5 to 8 carbon atoms or an aryl radical having from 6 to 14 carbon atoms. The aliphatic hydrocarbon radical can be linear or branched, saturated or unsaturated. Preferred cycloaliphatic hydrocarbon radicals are cyclopentyl or cyclohexyl radicals; preferred aryl radicals are phenyl or naphthyl radicals. In the case of T=xe2x80x94COOR5, S=COOaM or xe2x80x94COOR5. When both T and S are COOR5, the corresponding structural units are derived from dicarboxylic esters.
Apart from these ester groups, the structural units c) may also comprise other hydrophobic structural elements. These include polypropylene oxide or polypropylene oxide-polyethylene oxide derivatives of the formula 
x is from 1 to 150 and y is from 0 to 15. The polypropylene oxide(polyethylene oxide) derivatives can be linked via a group U1 to the ethyl radical of the structural unit c) corresponding to the formula IIIa, where U1=xe2x80x94COxe2x80x94NHxe2x80x94, xe2x80x94Oxe2x80x94 or xe2x80x94CH2xe2x80x94O. The structural unit is thus the amide, vinyl ether or allyl ether corresponding to the structural unit of the formula IIIa. R6 may in turn be as defined for R2 (see above) or be 
where U2=xe2x80x94NHxe2x80x94COxe2x80x94, xe2x80x94Oxe2x80x94 or xe2x80x94OCH2xe2x80x94, and S is as defined above. These compounds are polypropylene oxide(-polyethylene oxide) derivatives of the bifunctional alkenyl compounds corresponding to the formula IIIa.
As a further hydrophobic structural element, the compounds of the formula IIIa may contain polydimethylsiloxane groups, which in the formula IIIa corresponds to T=xe2x80x94Wxe2x80x94R7.
W is 
(hereinafter referred: to as a polydimethylsiloxane group), R7 can be as defined for R2 and r can be from 2 to 100.
The polydimethylsiloxane group can not only be bound directly to the ethylene radical of the formula IIIa, but also via the group xe2x80x94COxe2x80x94[NHxe2x80x94(CH2)3]sxe2x80x94Wxe2x80x94R7 or xe2x80x94COxe2x80x94O(CH2)zxe2x80x94Wxe2x80x94R7, where R7 is preferably as defined for R2 and s=1 or 2 and z=0 to 2. R7 may also be a radical of the formula 
The compounds are then bifunctional ethylene compounds of the formula IIIa which are linked to one another via the respective amide or ester groups, with only one ethylene group having been copolymerized.
A similar situation applies to the compounds of the formula IIIa,in which T=(CH2)zxe2x80x94Vxe2x80x94(CH2)zxe2x80x94CHxe2x95x90CHxe2x80x94R2, where z=0 to 4, V is either a polydimethylsiloxane radical W or a xe2x80x94Oxe2x80x94COxe2x80x94C6H4xe2x80x94COxe2x80x94Oxe2x80x94 radical and R2 is as defined above. These compounds are derived from the corresponding dialkylphenyldicarboxylic esters or dialkylenepolydimethylsiloxane derivatives.
Within the scope of the present invention, it is also possible for not only one but also both ethylene groups of the bifunctional ethylene compounds to be copolymerized. This gives structural units corresponding to the formula IIIb 
where R2, V and z are as defined above.
The fourth structural unit d) is derived from an unsaturated dicarboxylic acid derivative and has the formula IVa and/or IVb 
where a, M, X and Y are: as defined above.
According to the invention, the copolymers of the invention comprise from 51 to 95 mol % of structural units of the formula Ia and/or Ib and/or Ic, from 1 to 48.9 mol % of structural units of the formula II, from 0.1 to 5 mol % of structural units of the formula IIIa and/or IIIb and from 0 to 47.9 mol % of structural units of the formula IVa and/or IVb.
Preference is given to copolymers comprising from 55 to 75 mol % of structural units of the formula Ia and/or Ib, from 19.5 to 39.5 mol % of structural units of the formula II, from 0.5 to 2 mol % of structural units of the formula IIIa and/or IIIb and from 5 to 20 mol % of structural units of the formula IVa and/or IVb.
In a preferred embodiment, the copolymers of the invention further comprise up to 50 mol %, in particular up to 20 mol %, based on the sum of the structural units a to d, of structures which are derived from monomers based on vinyl or (meth)acrylic acid derivatives such as styrene, xcex1-methylstyrene, vinyl acetate, vinyl propionate, ethylene, propylene, isobutene, hydroxyalkyl (meth)acrylates, acrylamide, methacryl-amide, N-vinylpyrrolidone, allylsulfonic acid, methallylsulfonic acid, vinylsulfonic acid, vinylphosphonic acid, AMPS, methyl methacrylate, methyl acrylate, butyl acrylate, allylhexyl acrylate, etc.
The number of repeating structural units in the copolymers is not subject to any restrictions. However, copolymers having mean molecular weights of from 1000 to 100,000 g/mol have been found to be particularly advantageous.
The copolymers of the invention can be prepared in various ways. The important thing is that from 51 to 95 mol % of an unsaturated monocarboxylic or dicarboxylic acid derivative, from 1 to 48.9 mol % of an oxyalkylene alkenyl ether, from 0.1 to 5 mol % of a vinylic polyalkylene glycol, polysiloxane or ester compound and from 0 to 55 mol % of a dicarboxylic acid derivative are polymerized by means of a free-radical initiator.
As unsaturated monocarboxylic or dicarboxylic acid derivatives which form the structural units of the formula Ia, Ib or Ic, preference is given to using: acrylic acid, methacrylic acid, itaconic acid, itaconic anhydride, itaconimide and the monoamide of itaconic acid.
In place of acrylic acid, methacrylic acid, itaconic acid and the monoamide of itaconic acid, it is also possible to use monovalent or divalent metal salts, preferably sodium, potassium, calcium or ammonium salts.
If the acrylic, methacrylic or itaconic acid derivative is an ester, preference is given to using derivatives whose alcoholic component is a polyalkylene glycol of the general formula HOxe2x80x94(CmH2mO)nxe2x80x94R2, where R2=H, an aliphatic hydrocarbon radical having from 1 to 20 carbon atoms, a cycloaliphatic hydrocarbon radical having from 5 to 8 carbon atoms, a substituted or unsubstituted aryl radical having from 6 to 14 carbon atoms and m=2 to 4 and n=0 to 200.
Preferred substituents on the aryl radical are xe2x80x94OHxe2x80x94, xe2x80x94COOxe2x8ax96 or xe2x80x94SO3xe2x8ax96 groups.
The unsaturated monocarboxylic acid derivatives can be present only as monoesters, while in the case of the dicarboxylic acid itaconic acid, diester derivatives are also possible.
The derivatives of the formulae Ia, Ib and Ic can also be present as mixtures of esterified and free acids and are preferably used in an amount of from 55 to 75 mol %.
The second component used according to the invention for preparing the copolymers of the invention is an oxyalyklene glycol alkenyl ether which is preferably used in an amount of from 19.5 to 39.5 mol %. Preferred oxyalkylene glycol alkenyl ethers correspond to the formula V
CH2=CR3xe2x80x94(CH2)pxe2x80x94Oxe2x80x94(CmH2mO)nxe2x80x94R2
where R3=H or an aliphatic hydrocarbon radical having from 1 to 5 carbon atoms and p=0 to 3. R2, m and n are as defined above. The use of polyethylene glycol monovinyl ethers (p=0 and m=2) has been found to be particularly advantageous, with n preferably being from 1 to 50.
As third component used according to the invention for introducing the structural unit c), preference is given to using from 0.5 to 2 mol % of a vinylic polyalkylene glycol, polysiloxane or ester compound. Preferred vinylic polyalkylene glycol compounds are derivatives having the formula VI, 
where S is xe2x80x94H or COOaM and U1 is xe2x80x94COxe2x80x94NHxe2x80x94, xe2x80x94Oxe2x80x94 or xe2x80x94CH2Oxe2x80x94, i.e. the vinylic polyalkylene glycol compounds are the acid amide, vinyl or allyl ethers of the corresponding polypropylene glycol or polypropylene glycol-polyethylene glycol derivatives. x can be from 1 to 150 and y can be from 0 to 15. R6 can either be as defined for R1 or be 
where U2=xe2x80x94NHxe2x80x94COxe2x80x94, xe2x80x94Oxe2x80x94 or xe2x80x94OCH2xe2x80x94 and S=xe2x80x94COOaM and preferably xe2x80x94H.
In the case of R6=R2 and R2 preferably being H, the compounds are the polypropylene glycol(-polyethylene glycol) monoamides or ethers of the corresponding acrylic (S=H, R4=H), methacrylic (S=H, R4=CH3) or maleic (S=COOaMxe2x88x92R4=H) acid derivatives. Examples of such monomers are the N-(methyl-polypropylene glycol)monoamide of maleic acid, the N-(methoxy-polypropylene glycol-polyethylene glycol)-monoamide of maleic acid, polypropylene glycol vinyl ether and polypropylene glycol allyl ether.
In the case of R6xe2x89xa0R2, the compounds are bifunctional vinyl compounds whose polypropylene glycol(-poly-ethylene glycol) derivatives are joined to one another via amide or ether groups (xe2x80x94Oxe2x80x94 or xe2x80x94OCH2xe2x80x94). Examples of such compounds are polypropylene glycol bismaleamide, polypropylene glycol diacrylamide, polypropylene glycol dimethacrylamide, polypropylene glycol divinyl ether, polypropylene glycol diallyl ether.
As vinylic polysiloxane compound, preference is given to derivatives corresponding to the formula VII, 
where R4=xe2x80x94H or CH3, 
and r=2 to 100 and R7=R2. Examples of such monomers are monovinylpolydimethylsiloxane.
Further vinylic polysiloxane compounds which can be used are derivatives of the formula VIII, 
where s=1 or 2, R4 and W are as defined above and R7 can either be as defined for R2 or be 
and S is as defined above and is preferably hydrogen or xe2x80x94COOR5.
Examples of such monomers having a vinyl function (R7=R2) are polydimethylsiloxanepropylmaleamide or polydimethylsiloxanedipropyleneaminomaleamide. In the case of R7xe2x89xa0R2, the compounds are divinyl compounds such as polydimethylsiloxanebis(propylmaleamide) or polydimethylsiloxanebis(dipropyleneaminomaleamide).
As further vinylic polysiloxane compound, preference is given to using a derivative corresponding to the formula IX: 
where z is from 0 to 4 and R4 and W are as defined above. R7 can either be as defined for R2 or be 
where S is as defined above and is preferably hydrogen. Examples of such monovinylic compounds (R7=R1) are polydimethylsiloxane(1-propyl 3-acrylate) or polydimethylsiloxane(1-propyl 3-methacrylate).
In the case of R7xe2x89xa0R2, the compounds are divinyl compounds such as polydimethylsiloxanebis(1-propyl 3-acrylate) or polydimethylsiloxanebis(1-propyl 3-methacrylate).
Vinylic ester compounds used for the purposes of the present invention are preferably derivatives of the formula X, 
where S=COOaM or xe2x80x94COOR5 and R5 is an aliphatic hydrocarbon radical having from 3 to 20 carbon atoms, a cycloaliphatic hydrocarbon radical having from 5 to 8 carbon atoms or an aryl radical having from 6 to 14 carbon atoms. a and M are as defined above. Examples of such ester compounds are di-n-butyl maleate or fumarate or mono-n-butyl maleate or fumarate.
Furthermore, it is also possible to use compounds of the formula XI 
where z is from 0 to 4 and R2 is as defined above. V can also be as defined for W (i.e. a polydimethyl-siloxane group), which corresponds to a dialkenyl-polydimethylsiloxane compound such as divinylpoly-dimethylsiloxane. Alternatively, V can also be xe2x80x94Oxe2x80x94COxe2x80x94C6H4xe2x80x94COxe2x80x94Oxe2x80x94. These compounds are dialkenyl phthalic acid derivatives. A typical example of such a phthalic acid derivative is diallyl phthalate.
The molecular weights of the compounds which form the structural unit c) can be varied within wide limits and are preferably in the range from 150 to 10,000.
As fourth component for preparing the copolymers of the invention, preference is given to using from 5 to 20mol % of an unsaturated dicarboxylic acid derivative of the formula XIII:
MaOOCxe2x80x94CHxe2x95x90CHxe2x80x94COXxe2x80x83xe2x80x83XII
where a, M and X are as defined above.
When X=OMa, the unsaturated dicarboxylic acid derivative is derived from maleic acid, fumaric acid, monovalent or divalent metal salts of these dicarboxylic acids, e.g. the sodium, potassium, calcium or ammonium salt or salts with an organic amine radical. Monomers which form the unit Ia can further comprise polyalkylene glycol monoesters of the abovementioned acids having the general formula XIII:
MaOOCxe2x80x94CHxe2x95x90CHxe2x80x94COOxe2x80x94(CmH2mO)nxe2x80x94R2
where a, m, n and R2 are as defined above.
The fourth component can be derived from unsaturated dicarboxylic anhydrides and imides of the general formula XIV (5 to 20 mol %) 
where Y is as defined above.
In a preferred embodiment of the invention, further monomers as described above can be used in amounts of up to 50 mol %, preferably up to 20 mol %, based on the sum of the structural units a) to d).
The copolymers of the invention can be prepared by the customary copolymerization methods. A particular advantage is that, according to the invention, the copolymerization can be carried out without solvents or else in aqueous solution. In both cases, the reactions are carried out under atmospheric pressure and therefore do not pose a safety problem.
If the process is carried out in aqueous solution, the polymerization is carried out at from 20 to 100xc2x0 C. with the aid of a customary free-radical initiator, with the concentration of the aqueous solution preferably being set to from 30 to 50% by weight. In a preferred embodiment, the free-radical polymerization is carried out in the acid pH range, in particular at a pH of from 4.0 to 6.5,with conventional initiators such as H2O2 being able to be used without there being a risk of ether cleavage, as a result of which the yields would be greatly reduced.
In the process of the invention, preference is given to placing the unsaturated dicarboxylic acid derivative which forms the structural unit d) in partially neutralized form in aqueous solution, preferably together with the polymerization initiator, in a reaction vessel and introducing the remaining monomers as soon as the initial charge has reached the required reaction temperature. Polymerization aids which reduce the activation threshold of the preferably peroxidic initiator can be added separately, so that the copolymerization can occur at relatively low temperatures. In a further, preferred embodiment, the unsaturated dicarboxylic acid derivative and also the free-radical initiator are metered into the initial charge in the reactor in separate streams or in a common stream. This provides an ideal solution to the problem of heat removal.
However, it is also possible to place the polyoxyalkylene glycol alkenyl ethers which form the structural unit b) in the reaction vessel and to introduce the monocarboxylic or dicarboxylic acid derivative (structural unit a)) in such a way that a uniform distribution of the monomer units over the polymer chain is achieved.
The type of polymerization initiators, polymerization activators and other auxiliaries, e.g. molecular weight regulators, used is not critical. Initiators which can be used are the customary free-radical formers such as hydrogen peroxide, sodium, potassium or ammonium peroxodisulfate, tert-butyl hydroperoxide, dibenzoyl peroxide, sodium peroxide, 2,2xe2x80x2-azobis(2-amidinopropane) dihydrochloride, azobisisobutyro-nitrile, etc. If redox systems are used, it is, for example, possible to combine the above-mentioned initiators with activators having a reducing action. Examples of such reducing agents are Fe(II) salts, sodium hydroxymethanesulfinate dihydrate, alkali metal sulfites and metabisulfites, sodium hypophosphite, hydroxylamine hydrochloride, thiourea, etc.
A particular advantage of the copolymers of the invention is that they can also be prepared without solvents, which can be achieved with the aid of customary free-radical initiators at temperatures of from 60 to 150xc2x0 C. This variant is particularly advantageous for economic reasons when the copolymers of the invention are to be used directly in water-free form, because costly removal of the solvent, in particular water (for example by spray drying), then becomes unnecessary.
The copolymers of the invention are very useful as additives for aqueous suspensions of inorganic and organic solids, in particular those based on mineral or bituminous binders such as cement, plaster of Paris, lime, anhydrite or other building materials based on calcium sulfate, or based on pulverulent dispersion binders which are advantageously used in an amount of from 0.01 to 10% by weight, in particular from 0.05 to 5% by weight, based on the weight of the mineral binder. However, the copolymers of the invention can also be used very successfully in the fields of ceramic compositions, refractory compositions and oilfield chemicals.
The following examples illustrate the invention.